1. Field of the Invention
The present invention relates to an automatic transmission for vehicles. More particularly, the present invention relates to a shift control method for an automatic transmission in which a fill time is learned with the occurrence of interlocking generated during power-on upshifting, and the learned fill time is applied during a subsequent power-on upshifting operation such that interlock shock, which occurs at the end of shifting, is prevented.
2. Description of the Related Art
In the automatic transmission used for vehicles, a shift control system performs control to realize automatic shifting into different speeds and shift ranges according to various factors, including throttle opening, vehicle speed and load, and several other engine and driving conditions detected through a plurality of sensors. That is, based on such factors, the shift control system controls a plurality of solenoid valves of a hydraulic control system such that hydraulic flow in the hydraulic control system is controlled, resulting in the shifting of the transmission into the various speeds and shift ranges.
In more detail, when the driver manipulates a shift lever to a particular shift range, a manual valve of the hydraulic control system undergoes port conversion as a result of the manual valve being indexed with the shift lever. By this operation, hydraulic pressure supplied from a hydraulic pump selectively engages a plurality of friction elements of a gearshift mechanism according to the duty control of the solenoid valves, thereby realizing shifting into the desired shift range.
In such an automatic transmission, shift quality is determined by how smoothly the friction elements are engaged and disengaged. Namely, when changing shift ranges, the timing between the engagement of a specific set of friction elements in relation to the disengagement of another specific set of friction elements determines the shift quality of the automatic transmission. Accordingly, there have been ongoing efforts to develop improved shift control methods that enhance shift quality by better controlling the timing of friction elements to engaged and disengaged states.
The different kinds of automatic shifting operations that can be performed in a drive D range according to how the driver operates the vehicle include power-on upshifting, power-on downshifting, power-off upshifting, and power-off downshifting. The present invention relates to a method of controlling power-on upshifting.
In the prior art method, if a power-on upshift signal is input while the vehicle is being driven, power-on upshift control is performed using a pre-installed program. However, as a result of an imprecise clutch gap and a reduction in line pressure at the start of shifting, the timing of the release of clutch pressure and the application of clutch pressure do not correspond such that initial fill time learning is unstable. Accordingly, shift shock as a result of interlocking occurs at the end of shifting.
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide a shift control method for an automatic transmission in which control is performed according to learned conditions if power-on upshifting occurs, and depending on the degree of interlocking occurring at the end of shifting, it is determined if fill time learning has occurred. If fill time learning has occurred, it is used to reduce shift shock generated by interlocking at the end of shifting during a subsequent power-on upshifting operation.
To achieve the above object, the present invention provides a shift control method comprising the steps of (a) determining if an input shift signal is a power-on upshift signal; (b) determining if driving conditions satisfy power-on upshift learn conditions if the input shift signal is a power-on upshift signal; (c) performing power-on upshift control if power-on upshift learn conditions are satisfied; (d) learning an initial fill time and completing shifting; (e) determining if shifting is completed; (f) determining if run-up occurred during the shift operation if shifting is completed; (g) determining if interlocking occurred if run-up did not occur; (h) determining, if interlocking occurred, if the interlocking is above a predetermined level; and (i) learning a fill time if the interlocking is above the predetermined level.
According to a feature of the present invention, in step (h), if the interlocking is below the predetermined level the fill time is not learned.
According to another feature of the present invention, the learning of the fill time is performed by adding a learned initial fill time, which is learned during a present power-on upshift operation, to a previous initial fill time, which is learned during a previous power-on upshift operation.
According to yet another feature of the present invention, in step (g) of determining if interlocking occurred, if turbine rpm change dNt is less than target turbine rpm dNt1, it is determined that the interlocking is severe.